Snap-action switches having booily shifting of the line of tension of the strand portion



Oct. 13, 1964 L. STRAUSS ETAL 3,153,125

SNAP-ACTION swncnss HAVING sonny SHIFTING OF THE mm: 0? TENSION OF THE STRAND PORTION Filed April 6. 1961 l l i! 55 l I i I INVENTORS LEOPoLD STRAUSS BY enw/uw woJ'c/K United States Patent 6'Claims. c1. Zed-113) This invention relates to a new and improved snapaction switch device and more particularly to a device especially suitable for use, for example, as a flasher switch in signalsystems of motor vehicles.

This invention provides modifications or improvements of the switch device disclosed in co-pending United States patent application, Serial No. 825,681, filed iuly 8, 1959, new US. Patent No. 3,090,851.

The switch device of that application includes a switching member comprising a strand portion held in tension by and holding elastically bowed a cantilevered tongue portion so that when an electrical current is passed through the strand portion, thereby heating it and causing it to elongate, the tongue portion causes a movable free end formed by united ends of the strand and tongue portions to move to a new position with a snap action. The

embodiment particularly described and illustrated in said application is eminently suitable for use as a flasher switch in a D.C. circuit having a substantially fixed line load. However, where it is used in circuits having different or variable line loads, the frequency of its snap action I of construction and operation disclosed in said co-pending application, will operate at a substantially uniform frequency irrespective of wide variations in the line load on the circuit in which the device is employed.

A further object is to provide a simple, sturdy and economical construction of a snap-action switch device, and one which is positive, efficient and reliable in its operation.

According to one feature of the present invention, there is provided a switch device of the general type disclosed in the co-pending application, wherein movements of the switching member are initiated, not by elongation or contraction of the strand portion relative to the tongue portion, but rather by a bodily shifting of the line of tension of the strand portion relative to the tongue portion, and wherein, although the means for producing the shifting is connected in the circuit employing the switch device, the operation of that means is not varied ap- According to another feature of this invention, there I is provided, for snap-action switch devices of the character described, a distinctive frame member uniquely assembled with the switching member and with other elements to constitute the operative switch device.

The invention provides a switch device which includes a trame, a switching member having an elongated strand portion and an elongated tongue portion united at one end thereof to form a free end of the member, means mounting the other end of the tongue portion in canti levered relation to the frame, and means securing the other end of the strand portion to the frame to one side of the cantilevered end of the tongue portion with the strand portion holding the tongue portion bent elastically Patented Get. :13, 1%54 "ice between its ends in a reversely elastically curved formation crossing the line of tension of the strand portion with a first part of theformation curving in one direction only to that line from the cantile ered end so that this first part continuously exerts only a unidirectional moment urging the free end of the switching member in the direction opposite to the direction of curvature of the first part, and with another part of this formation curving oppositely into and joined with the free end of the switching member from the other side of that line, whereby the line of tension of the strand portion is normally held to one side of a point of zero moment on the tongue portion so as to bias the free end of the switching member to one switch position. With the foregoing elements, further means are provided which bear upon a part of the strand portion between its fixed end and the point of crossing of its line of tension by the tongue portion and serve normally to displace the strand portion angularly so as to hold its line of tension to the other side of the point of zero moment on the tongue portion, whereby the free end of the switching member is held in a second switch position against the normal action of the strand and tongue portions, together with means for rendering the displacing means ineffective so that the switching member itself then will move the free end quickly to said one position.

The invention further provides an arrangement or combination of parts which includes a frame of generally planar form having a backward portion providing a first "support surface and a second support surface ahead of and spaced from the plane of the first surface, with the strand portion fixed to the support surf cc and the tongue portion fixed to the second support surface in cantilevered relationship thereto. j

Other features, objects, and advantages of the invention will be apparent from the following detailed description of a preferred embodiment thereof and from the accompanying illustrated drawings in which:

FIG. 1 is. a side elevational View, partly in section, of the switching device;

FIG. 2 is a front elevational View of the switch device, including a schematic diagram of a typical DC. circuit in which the device may be employed;

FIG. 3 is a schematic, fragmentary isometric view of the device.

Referring to the drawings and particularly to FIG. the switch device of the illustrated embodiment includes a switching member 165,21 frame member Gil, and a bridge member 78. The switching member 19 comprises a uni tary elongatedpiece of thin resilient electrically conduc-' tive strip material. it is formed with a strand or tension portion composed of spaced parallel side strands 11 and 12, and with a central tongue or compression portion 14 which is spaced between the side strands and has one of its ends joined or integral with the strands at one end of the latter to constitute a free end of the switching member as seen as 15. The said free end 15 carries a contact element 51. The strands ll and 12 are joined together at their other ends by a base portion 16 of the piece, which portion is spaced from the inner end 17 of tongue M- by a cut-away area it; that separates the central tongue from the other portions of the switching member, except at the free end 15.

Member 16 may be formed in a single operation by pressing or stamping it as a unit from a thin strip of the desired material.

The frame member 6t), shown most fully in F188. 1 and 2, is of generally planar form and comprises spaced substantially parallel longitudinal portions 61 and 62, i aving strengthening flanges 63 and 6 and integral forward and rearward end portions 65 and as. The end portions 65 and as rigidly interconnect and define with the longitudinal portions a substantially rectangular frame, encompassing an open area 67.

End portion 66 provides a first support surface ss, including in this embodiment two segments which together have an overall width approximating that of the switching member ill, and a second support surface 69 having a width approximating that of the tongue 14. These surfaces are formed, in the embodiment shown, by pressing material outwardly from the plane of the said end portion, as indicated in FIG. 3. Surface so is disposed forwardly and centrally of surface 68 and is pressed outwardly by a greater distance than surface 63.

The inner end T37 of tongue 14 is fixed in face-to-face relation to the surface 69, as by welding, in cantilevered relationship thereto, and the inner ends of the spaced side strands 11 and 12 are fixed, as by welding, to respective segments of the surface 68. Thus, the body of tongue 14 extends freely away from its cantilevered end toward the forward end portion 65 and into the said open area 67, and the strands ill and i2 flank the elevated surface 69 and extend to a fixed location backward from it. The surface ea is spaced forwardly of the surface 68 a certain distance so that when the tongue and the strands are properly positioned on and fixed to these surfaces, the end 17 of the tongue is displaced forwardly from base 16 of member lit, and the body of the tongue between cantilevered end 1'7 and free end 15 is held by the strands in an elastically bowed formation to that side of the cantilevered surface 69 occupied by the line of tension or plane of the strands l1 and 12. The tongue thus is held continuously in an elastic curvature of 8 form extending from the cantilevered end on the surface 69 in an arc 14a toward the line of tension of the strands, then across that line and thence in an oppositely curved arc 14b into the free end 15 of the switching member, as seen in FIG. 3.

The bridge member '79 is a rigid piece of metal forming spaced elongated foot portions 1, an upright arm portion 72, and a span portion '73. The foot portions 71 are joined, as by welding, flush to portions of the strands ill. and 12 extending between a location near the fixed ends of the strands and the point of the crossing of their line of tension by the tongue. The upright arm portion 72 extends transversely from and rigidly interconnects the backward ends of the foot portions, while the span portion 73 is elevated so as to clear the tongue 1d and rigidly interconnects the forward ends of the foot portions.

The arm 72 is formed with an aperture at 74 to receive a thermally expansible electrical resistance wire 76 passed therethrough, and with a spherical surface at its backward side to seat a bead 75 of glass or other dielectric material fixed to the resistance wire. The wire 76 has one of its ends secured to an upstanding arm 77 on the forward end portion d of the frame as, from which a length of the wire constituting an actuating portion 79 is stretched rearwardly through the aperture 74 in upstanding arm 72 through and to the bead 75. From the bead the wire extends across end portion es and upwardly through an aperture in an electrically insulating partition 81 (FIG. 1) and thence forwardly in the form of a ballast resistance coil St anchored at its forward end to a projection 75 which is mounted on but electrically insulated from the forward end portion of the frame. The partition 3. is a sheet of mica or other suitable insulating material which shields the ballast coil from the switching member and the frame.

Contact or stop elements 82 and 85 (FIG. 1) are disposed at opposite sides of the free end of the switching member it) in the path of movement thereof, so as to limit its switching movements.

The element 82 is held in the desired position by a backwardly projecting portion of a plate member 84 which is fixed to the forward end portion 65 of the frame in electrical connection therewith.

The element 35 is carried on a contact arm $3 which is held in the desired position by a backwardly projecting portion as of a plate member $57 of which the aforementioned projection 78 is an integral upright extension. The plate member $7 is fixed to the forward end portion of the frame but is electrically insulated from it, as by layers 88 of mica or other similar dielectric material, wrapped around member'87. These insulating layers lie between the juxtaposed members 84 and 8'7 and between member 37 and a pair of clamping flanges 39 which are formed as integral portions of the frame member and serve to fasten the mounting plates of the two stop elements securely in place on the forward frame portion 65.

A relatively heavy wire 90, of copper or other conductive material is secured to the contact arm 33, as by welding, and extends from it backwardly and thence latorally across end portion' to a point of connection, as by welding, to a terminal 91. The terminal 91 passes through a base plate 92 formed of a suitable dielectric material, to which this terminal is secured by means of clamping tongs '93 integral with the terminal. The base plate is disposed transversely of the plane of the frame 60. An extension 94 integral with the backward end portion of the frame so extends over the face of the base plate 92, being fixed thereto bya rivet 96, and passesthrough the base plate to form a second terminal member 95. The base plate electrically insulates the terminals, one from the other, supports the elements of the switch device, and further serves as the support for a cover 97, shown in phantom lines in FIGS. 1 and 2,-which is formed as an'inverted cup enclosing'the switch device and has an annular edge portion 98 receiving the circular edge of base plate 92.

In the absence of the tension of the stretched wire length 79 upon the switching memberl'll, the point of zero moment on the tongue 14 is located to the left hand side of the line of tension of the strands 11, 1-2, as these elements are viewed in FIG. 1, and the free end 15 is then biased in a clockwise direction by the elastic unbending moment of the portion of the tongue near'the cantilevered tongue end, so that the contact element '51 then bears against stop element 85. The stretched or actuating portion 79 of the wire, however, normally applies through the bridge member a leverage acting upon the strands l1, 12 with a force sufiicient to displace'the strands angularly relative to their fixed ends and thereby displace the line of tension of the strands to the other side of the point of zero bending movement on the tongue, so that the free end of the switching member is displaced counterclockwise to a position in which it bears against the stop element 82. That is its position when the wire portion 79 is in its normal or cold condition.

The wire 76 is made of a material having a very considerable electrical resistance and a high coefficient of thermal expansion, so that upon the passagethrough said portion 79 of a current within a predetermined ampere range, the length of the wire in the portion 79 increases rapidly to such an extent that the tension on the bridge member '79 and the leverage of the latter on the strands are relieved. The free end 15 of the switchingmember 14 then snaps to the position in which it bears against element under the bias of the tongue and strands. This action occurs when a circuit is established to the terminals 91 and 95 whereupon current can flow only through the resistance 76. The parts of the device then assume the position in which they are seen in FIG. 1. As soon, however, as they assume that position, the current from or to terminal 91 is largely shunted away from thewire '76 by flowing directly through contacts 85 and 51 and the body of the switching member 10, which in this embodiment is always in electrical connection with the frame 6%) and the terminal 95. The wire portion 79 then cools quickly and contracts so as to restore a tension on the arm 72 of the bridge member sufiicient to restore the free end 15 to its original position.

The free end 15 thus snaps back and forth between its two limiting positions as long as an energizing circuit is kept closed to the two terminals. Moreover, the energizing circuit can be one carrying electrical loads of varying magnitude, without adversely affecting the frequency or the effectiveness of the snap action of the device. An illustrative circuit of this type is shown in FIG. 2, wherein conductors 101 lead to the two terminals 91 and 95 from a sourceof direct current 102 and any desired number of light bulbs or other resistance loads 103 may be connected in parallel in the circuit by the closing of switches 104. The magnitude of the current flowing through the switch device varies of course with variations in the number of switches 104 closed; but such variations in the magnitude of the current flow do not materially affect the operation of the switch device since the actuating portion '79 is a part of a current path through the wire 76, including the ballast coil 80, having a resistance many times greater than the highest resistance ofiered by the bulbs in the circuit and so great that portion 79 is quickly elongated to the required extent by the amount of current flow obtained through it when any number of the bulbs is active in the circuit.

Thus, the switch device of the present invention is eminently suitable for use as a flasher switch in an electrical circuit containing a variable or indeterminate number of light bulbs. Such circuits are encountered, for example, in the signal systems of motor vehicles, particularly trucks, and in the control systems for theater marquees.

The switch device of the present invention is of course not limited in its application to circuits having a variable load line, nor is its use restricted to a flasher. While the device is shown in FIGS. 1 and 2 as being vertically disposed, it is not restricted to any particular directional disposition. The new features of the invention can be utilized in various ways and are not restricted to the illustrated embodiment except as required by a fair construction of the appended claims.

What is claimed is:

1. In a switch device, a frame constituted by a formed unitary piece of rigid sheet metal having substantially parallel side portions and forward and backward portions rigidly joining ends of said side portions, said portions defining an open area therebetween, said backward portion providing a first support surface near the rear thereof and a second support surface near the front and centrally thereof at a greater distance from the plane thereof than said first support surface, a switching member comprising an elongated strand portion and an elongated tongue portion, said strand and tongue portions being united at one end thereof to constitute a free end of said member, means anchoring the respective other ends of said strand and tongue portions in relatively fixed positions on said first and second support surfaces, respectively, with said strand portion under tension and said tongue portion under compression between the respective fixed ends and said free end, the fixed end of said tongue portion being cantilevered on said second support surface, said tongue portion being bent elastically between its ends into a reversely elastically curved formation which crosses the line of tension of said strand portion with a first part of said formation curved elastically in one direction only from said cantilevered end to said line of tension so that said first part continuously exerts only a unidirectional moment urging said free end in the direction opposite to the direction of its curvature, and with another part of said formation curved oppositely into and joined with said free end from the other side of said line, said portions coacting to bias said line of tension toward one side of a point of zero moment on said tongue portion and thereby bias said free end toward one switch position, means bearing upon said strand portion to constrain it to a position in which said line of tension is on the other side of said point and said free end is held in a second switch position, and means for rendering said constraining means ineffective so that by the unbending moment of said first part said line of tension is biased to said one side and said free end moved to said one switch position, said constraining means comprising an arm secured to and extending transversely away from a part of said strand portion between said fixed end thereof and the point of the crossing of its line of tension by said tongue portion and a thermally expansible elongated electrical resistance element secured to said arm and normally held under a tension effective to constrain said strand portion to its said position, and said means for rendering said constraining means ineffective comprising means for passing an electrical current through said element to heat and lengthen said element.

2. In a switch device, a frame of generally planar form constituted by a formed unitary piece of rigid material having a backward portion providing a first support surface and a second support surface spaced from the plane of said first support surface, a switching member comprising an elongated piece of resilient flat strip material having portions of its body cut away along its opposite sides to leave integrated at one end thereof substantially parallel side strands and a central tongue extending from said one end between said side strands and joined thereto only at said one end, said one end constituting a free end of said member movable transversely relative to said frame, the other ends of said strands being fixed to the said first support surface and the other end of said tongue being fixed to said second support surface in cantilevered relationship thereto, said tongue being elastically bent between its ends into a curvature continuously held in compression by, and crossing the line of tension of, said strands and continuously holdingsaid strands in tension.

3. In a. switch device, a frame of generally planar form constituted by a formed unitary piece of rigid sheet metal having a backward portion providing a first supportsurface and a second support surface ahead of, and spaced from the plane of, said first support surface, a switching member comprising a unitary elongated piece of resilient flat strip material having portions of its body cut away along its opposite sides to leave integrated at one end thereof substantially parallel side strands and a central tongue extending from said one end between said side strands and joined thereto only at said one end, said one end constituting a free end of said member movable transversely relative to said frame, the other ends of said strands being fixed to said first support surface and the other end of said tongue being fixed to said second support surface in cantilevered relationship thereto, said frame having a forward portion thereof spaced ahead of said free end, and stop elements mounted on said forward portion and projecting at opposite sides of said free end into the path of movement of said free end to limit such movement in both directions, said support surfaces being constituted by bosses pressed out of said backward portion to one side of the plane thereof, two of said bosses being laterally spaced apart near the rear thereof to constitute said first support surface and one of said bosses being centrally disposed near the front thereof, and at a greater elevation from the plane thereof, to constitute said second support surface.

4. In a switch device, a frame of generally planar form constituted by a formed unitary piece of rigid sheet metal having a backward portion providing a first support surface and a second support surface ahead of, and spaced from the plane of, said first support surface, a switching member comprising an elongated piece of resilient flat strip material having portions of its body cut away along its opposite sides to leave integrated at one end thereof substantially parallel side strands and a central tongue extending from said one end between said side strands and joined thereto only at said one end, said one end constituting a free end of said member movable transversely relative to said frame, the other ends of said strands 2 being fixed to said first support surface and the other end of said tongue being fixed to said second support surface in cantilevered relationship thereto, said frame having a forward portion thereof spaced ahead of said free end, stop elements mounted on said forward portion and projecting at opposite sides of said free end into the path ofmovement of said free end to limit such movement in both directions, said strands holding said tongue bent elastically in a curvature of S form extending from said cantilevered end in one direction of bending only toward and across the plane of said strands and thence in a reverse bend back into said free end, whereby said free end is normally biased to contact with one of said stop elements, first and second upstanding members rigidly secured, respectively, to said forward portion and to lengths of said strands disposed away from but near the fixed ends thereof, and a thermally expansible electrical resistance wire normally tensioned between said upstanding members so as to displace said strand lengths angularly from their normal position so that they hold said free end against another of said stop elements.

5. The device of claim 4, said second upstanding member comprising a span portion extending across said tongue in spaced relation thereto, a pair of rigid elongated foot portions extending along and fixed in face to face relationship to said strand lengths, and an upright arm portion integral with said foot portions, said span portion and'said' arm portion rigidly interconnecting said foot portions.

6. In a switch device, an elongated rigid frame of generally planar form constituted by a formed unitary piece of rigid material having spaced, substantially parallel longitudinal portions and front and rear portions rigidly joining ends of said longitudinal portions, said portions defining therebetween an open area, a switching member mounted on said rear portion and extending into said area, said switching membercomprising a unitary elongated piece of thin resilient strip material having portions of its body cut away along its opposite sides to leave integrated at one end thereof substantially parallel spaced side strands and a central tongue extending from one end along and-between said strands and joined to said strands only at said one end, said one end constituting a free end of said member movable transversely relative to said frame, said rear portion providing a first support surface and a second support surface disposed ahead and centrally of, and in a plane spaced from the plane of, said first support surface, the ends of said strands away from said free end being fixed to the said first surface and the end of said tongue away fromsaid free end being mounted on said second surface in cantilevered relationship thereto, said strands holding said tongue bent elastically between its ends in a curvature of 8 form extending from saidcantilevered endin one direction of bending only toward andacross the plane of said strands and thence in a reverse bend back into said free end, and stop elements mounted on saidfront end portion and projecting into said open area at opposite sides of said free end to limit the transverse movement of said free end.

References Cited'in the file of this patent UNITED STATES PATENTS 1,960,020 McGall May 22, 1934 2,308,522 Leuthold' Jan. 19, 1943 2,663,770 COX Dec. 22, 1953 2,701,475 Readeker Feb. 8, 1955 2,761,931 Schmidinger Sept. 4, 1956 3,090,851 Strauss-ct al; May 21, 1963 FOREIGN PATENTS 448,747 Italy May 25, 1949 

2. IN A SWITCH DEVICE, A FRAME OF GENERALLY PLANAR FORM CONSTITUTED BY A FORMED UNITARY PIECE OF RIGID MATERIAL HAVING A BACKWARD PORTION PROVIDING A FIRST SUPPORT SURFACE AND A SECOND SUPPORT SURFACE SPACED FROM THE PLANE OF SAID FIRST SUPPORT SURFACE, A SWITCHING MEMBER COMPRISING AN ELONGATED PIECE OF RESILIENT FLAT STRIP MATERIAL HAVING PORTIONS OF ITS BODY CUT AWAY ALONG ITS OPPOSITE SIDES TO LEAVE INTEGRATED AT ONE END THEREOF SUBSTANTIALLY PARALLEL SIDE STRANDS AND A CENTRAL TONGUE EXTENDING FROM SAID ONE END BETWEEN SAID SIDE STRANDS AND JOINED THERETO ONLY AT SAID ONE END, SAID ONE END CONSTITUTING A FREE END OF SAID MEMBER MOVABLE TRANSVERSELY RELATIVE TO SAID FRAME, THE OTHER ENDS OF SAID STRANDS BEING FIXED TO THE SAID FIRST SUPPORT SURFACE AND THE OTHER END OF SAID TONGUE BEING FIXED TO SAID SECOND SUPPORT SURFACE IN CANTILEVERED RELATIONSHIP THERETO, SAID TONGUE BEING ELASTICALLY BENT BETWEEN ITS ENDS INTO A CURVATURE CONTINUOUSLY HELD IN COMPRESSION BY, AND CROSSING THE LINE OF TENSION OF, SAID STRANDS AND CONTINUOUSLY HOLDING SAID STRANDS IN TENSION. 